There are a number of fields of application for ceramics including traditional ceramics such as pottery and fine china; refractories; industrial ceramics such as abrasives and grinding wheels and technical ceramics. Technical ceramics are ceramics having a high purity. They are used in a number of applications including substrates for electrical circuits and mechanical parts.
There are several major processes currently used in manufacturing ceramics.
In several of these processes, a liquid based ceramic composition containing a binder is dried. The dried composition is then subjected to a compaction step such as dry pressing, roll compaction or injection molding.
In fluid compositions which are to be dried, the liquid phase has generally been water if a water soluble binder has been used or a volatile organic solvent for water insoluble binders. These organic solvents are relatively expensive; should not be released to the environment and may present a fire hazard. Polyvinylbutyral in a solvent is typical of such systems and is used in tape casting. Polyvinylalcohol has been used in aqueous based binder systems for dry pressing. Unfortunately, polyvinylalcohol is hygroscopic and spray dried ceramic particles coated with polyvinylalcohol tend to pick up moisture from the environment, thus reducing the free flowing nature of the ceramic powder.
U.S. Pat. No. 3,472,803 issued Oct. 14, 1969 assigned to Corning Glass Works discloses a ceramic composition for slip casting which comprises 70 to 83 percent of a ceramic material, 4 to 12 percent of a binder which is a copolymer of styrene and butadiene. Preferably the compound contains a sodium salt of a polyacrylic acid optionally in combination with triethanol amine.
U.S. Pat. No. 3,991,029 issued Nov. 9, 1976 assigned to E. I. DuPont de Nemours and Company discloses a ceramic compound for tape casting comprising an internally plasticized thermosetting resin. The polymers contain a self crosslinking monomer selected from the group consisting of glycidyl methacrylate and the n-methylol amides of acrylic or methacrylic acid.
Chemical Abstract 102:11330h of Japanese Kokai 59,121,152 [84,121,152] discloses the use of an aqueous based ceramic slip containing from 5 to 20 parts by weight of a copolymer of one or more of acrylic and methacrylic acid and one or more of C.sub.1-18 mono or polyhydric alcohol esters of (meth)acrylic acid in a weight ratio of 50:50 to 99:1. The esters have a molecular weight of from 20,000 to 500,000 and are used in conjunction with an organic plasticizer, such as di-butyl phthalate.
U.S. Pat. No. 4,329,271 issued May 11, 1982 to GTE Products Corporation disclosed a process for tape casting using water soluble polymers. The present invention contemplates the use of polymer emulsions in water.
Derwent Accession No. 85-192624/32, an abstract of Japanese Kokai 60/118676 discloses a hot isostatic pressing of a uniform mixture of from 5 to 300 parts by volume of a thermoplastic material such as wax or polyethylene and 100 parts by volume of a ceramic. The soft binder permits the deformation of the ceramic mixture under a fluid pressure medium for the shaping of complex parts.
The references do not describe the use of an aqueous emulsion of a polymeric binder nor do they describe the type of treatment contemplated in the present invention.